Palaeomagnetic constraints on lower oceanic crustal processes (IODP Expedition 345 Hess Deep Plutonic Crust

大洋中脊海底扩张形成大洋岩石圈是地球上运行的基本地质过程之一。最重要但也是最棘手的问题之一是了解山脊下的岩浆库是如何形成下地壳的，特别是在快速扩张的速度下。来自下地壳的辉长岩通常是无法接触到的，但在构造上暴露在太平洋赫斯深裂谷的侧翼。IODP探险345旨在提供来自该地区的一套独特的下层大洋地壳样本，这些样本将深入了解海底扩张所涉及的岩浆和构造过程。作为这项工作的一部分，将从打捞到的岩心碎片中收集古地磁数据，这将对了解该地点下地壳的演化至关重要。这些数据将提供有关锁定在我们预计会遇到的辉长岩中的磁化方向和强度的宝贵信息，提供一个标记，可用于推断影响该地点的构造旋转量，并深入了解较低地壳岩石对海洋磁异常的贡献。此外，我们打算结合古地磁数据和井壁内部的地球物理图像，重新确定通过钻井恢复的一些岩芯的方向，从而使其他定向属性(例如结构数据)恢复到正确的地理参考框架。

Generation of ocean lithosphere by seafloor spreading at mid-ocean ridges is one of the fundamental geological processes operating on Earth. One of the most important yet most intractable problems is to understand how the magma reservoir beneath ridges generates the lower crust, especially at fast spreading rates. Gabbroic rocks from the lower crust are normally inaccessible, but are exposed tectonically on the flanks of the Hess Deep rift in the Pacific Ocean. IODP Expedition 345 aims to provide a unique suite of lower oceanic crustal samples from this locality that will yield insights into magmatic and tectonic processes involved in seafloor spreading. As part of this endeavour, palaeomagnetic data will be collected from recovered core pieces and will be critical to understanding the evolution of the lower crust at this site. These data will provide valuable information on the direction and strength of magnetization locked into the gabbroic rocks we expect to encounter, providing a marker that can be used to infer the amount of tectonic rotation that has affected the site and insights into the contribution that lower crustal rocks make to marine magnetic anomalies. In addition, we intend to use a combination of palaeomagnetic data and geophysical images of the inside of borehole walls to reorient some of the core pieces recovered by drilling, thereby allowing other directional properties (e.g. structural data) to be restored to the correct geographical reference frame.